Thirty subjects will be enrolled into this open label study. At entry into the study, anthropometric measures (wt, ht, waist, hip), body composition, respiratory quotient (RQ), resting energy expenditure (REE), and measures of food intake, hunger, and physical activity will be assessed. Additionally, the Positive and Negative Symptom Scale (PANSS) will be used to assess clinical status and all women will have a blood pregnancy test as required prior to having a DXA scan. Following completion of these assessments, subjects will begin a two week cross-taper from their current antipsychotic to aripiprazole. Psychiatric symptoms, weight, medical status and medication query will be reassessed after 2, 4, 8 and 12 weeks. RQ and hunger will be reassessed at the 4 week time point. Fasting bloodwork, pregnancy test, urine drug screen, vital signs, and all baseline assessments will be repeated at the 12 week time point or at early termination. During the study, dosage of aripiprazole will be tailored to each subject's need based on symptoms and side effects, and will remain at or below the maximum recommended dosage.